This invention relates to aluminum dross and more particularly, it relates to the use of oxide products or non-metallic products (NMP) recovered from aluminum dross.
Aluminum dross results from the melting of aluminum scrap such as used beverage containers, aluminum siding, castings and the like and treating the melt with salt flux. The flux accumulates on top of the melt and forms a dross or skim which contains aluminum, oxides of aluminum and oxides of elements such as magnesium and silicon and other alloying elements present in the various alloys. The dross is removed or skimmed from the melt and processed usually to recover the metallic aluminum occluded in the oxides. The aluminum can constitute 5 to 70% of the dross. Usually, the aluminum, which is considered the most valuable component, is recovered from the solidified dross by first fracturing it, for example, by ball milling. Thereafter, the fractured dross is heated in the presence of additional salt flux to free the metallic aluminum. The molten salt flux aids in releasing the molten aluminum from the dross. The salt flux is usually comprised of sodium chloride and potassium chloride. After the metallic aluminum is removed, the dross is comprised of salt flux and an insoluble constituent comprised largely of aluminum oxide, silicon oxide and magnesium oxide, often referred to as salt cake. Also, included in the salt cake are minor amounts of oxides of titanium oxide, copper oxide, zinc oxide, sulfur oxide, potassium oxide and sodium oxide. The titanium, copper and zinc oxide can be present from alloying elements in the aluminum scrap. It is desirable to recover all useful constituents from the salt cake. Thus, to avoid leaching of soluble salts from salt cake in landfills, the salt cake is treated to recover the salts in the salt flux and recover it from the insoluble constituents or non-metallic product. The salt cake can be advantageously treated in accordance with the procedures set forth in U.S. Pat. Nos. 5,102,453 and 5,227,143. However, even after such treatment, there remains the insoluble constituent or non-metallic product. U.S. Pat. No. 5,102,453 discloses the problems attendant the presence of magnesium from magnesium-containing alloys and the problems resulting from the addition of magnesium chloride to the recovery system. Namely, such addition increases the overall amount of magnesium chloride contained in the unrecoverable material or non-metallic product and even when disposed of in plastic film-lined landfills, problems still result. Thus, often the process of leaching the salt cake is not optimized to avoid disposal problems with non-metallic product.
Thus, it will be seen that there is a great need for a process that enables the recovery of the non-metallic product thereby recovering all the constituents from the aluminum dross and avoiding any dumping of NMP in landfills. The present invention provides such a process.